This invention relates to a catalyst composition for use in the production of methanol, and methanol and higher alcohol mixtures from synthesis gas.
Methanol has in the past been produced from exposure of synthesis gas to a alkali-free, copper-zinc oxide-based catalyst. In a similar manner, higher alcohols, primarily isobutanol, can be produced by an alkali promoted copper-zinc oxide catalyst. In addition, linear alcohols can be produced by copper-based catalysts composed of a mixture of several metals including ruthenium, cobalt, chromium and thorium. Synthesis gas is mainly a combination of H.sub.2 and CO.
Interest in these processes has increased with the advent of alcohol-gasoline fuel mixtures. Further, it has been found improved results in gasoline mixtures occur within a mix of methanol and higher aliphatic alcohols, or higher aliphatic alcohols alone.
A disclosure demonstrating a process to produce methanol is found in U.S. Pat. No. 3,326,956 by Davies and Snowden. Synthesis gas is passed over a catalyst containing copper, zinc and chromium oxides. Also, U.S. Pat. No. 4,565,802 by Suhoenthal and Slaugh gives the elements copper, zinc and aluminum as the catalyst. Both are incorporated herein by reference and teach that care must be taken to eliminate electrolytes such as alkali metal in order to produce highly active and selective catalysts.
The productivity normalized to surface areas for these types of catalysts are typically 2 to 5.times.10.sup.-5 by methanol per hour per m.sup.2.
A disclosure demonstrating a process to produce a mixture of methanol and higher alcohols is found in U.S. Pat. No. 4,122,110 by Sugier, et al. Synthesis gas is passed over a catalyst having the four elements copper, cobalt, an alkali metal and a metal selected from chromium, iron, vanadium, and manganese to produce methanol and higher alcohols. Production is reported to be higher than 100 Kg of C.sub.2 + or higher alcohols per cubic meter of catalyst with selectivity to alcohols 95% or higher, selectivity to linear saturated alcohols of C.sub.2 or more often higher than 70% by weight using the preferred method. The production rate to methanol plus higher alcohols is about 1.times.10.sup.-5 Kg per m.sup.2 per hour.
A catalyst comprising cobalt, and one or more of copper, silver, gallium, zirconium, zinc and thorium; one or more of palladium, platinum, and nickel; and one or more alkali metals was also recently disclosed by Nay et al. in U.S. Pat. No. 4,576,968. This catalyst is used with synthesis gas to obtain saturated straight-chain primary alcohols such as methanol, ethanol, propanol and butanol.
These attempts to improve higher alcohol production all require that the copper and an alkali metal be combined with a number of other elements. This expensive catalyst mixture is quite complex and requires great care in preparation to ensure the appropriate form is produced.
The catalysts demonstrated in the production of methanol, on the other hand, do not use alkali metals but require copper be combined with at least one other element.
This invention is premised on the discovery that copper may be used alone as the catalyst, employing only a small amount of an alkali promoter selected from Group IA elements.
Methanol may be produced exclusively or a methanol-higher alcohol mixture may be produced depending on the choice of alkali metal and reaction conditions. For example, a copper./potassium catalyst can produce methanol at a rate (based upon surface area) of 2 to 5 times greater than obtained with a copper-zinc oxide catalyst impregnated with cesium. It is demonstrated that the promotional effect increases monotonically from lithium to cesium, with the largest jump between sodium and potassium. Copper promoted with lithium can produce methanol and linear, higher alcohols yielding 30 percent by weight ethanol and higher alcohols. The surprising advantages occur from using only copper combined with the Group IA element, making the catalyst easier to produce and providing for a variety of ways in which to make the catalyst.
Accordingly, it is an object of the invention to provide a catalyst composition and method of producing and using the same suitable for use in producing methanol or methanol and higher alcohols, using copper along with a Group IA element promoter.
Another object is to provide a catalyst method of producing and using the same which is highly selective for C.sub.2 + alcohols.
Another object of the invention is to provide a catalyst and method of producing and using the same which is highly selective for methanol.
A further object is to provide a catalyst which is easy to produce.